Project description

Introduction to Adafruit’s PCF8523 Real Time Clock (RTC) Library

This is a great battery-backed real time clock (RTC) that allows your
microcontroller project to keep track of time even if it is reprogrammed,
or if the power is lost. Perfect for datalogging, clock-building, time
stamping, timers and alarms, etc. Equipped with PCF8523 RTC - it can
run from 3.3V or 5V power & logic!

The PCF8523 is simple and inexpensive but not a high precision device.
It may lose or gain up to two seconds a day. For a high-precision,
temperature compensated alternative, please check out the
DS3231 precision RTC.
If you need a DS1307 for compatibility reasons, check out our
DS1307 RTC breakout.

Dependencies

Usage Notes

Basics

Of course, you must import the library to use it:

importbusioimportadafruit_pcf8523importtime

All the Adafruit RTC libraries take an instantiated and active I2C object
(from the busio library) as an argument to their constructor. The way to
create an I2C object depends on the board you are using. For boards with labeled
SCL and SDA pins, you can:

fromboardimport*

You can also use pins defined by the onboard microcontroller through the
microcontroller.pin module.

Now, to initialize the I2C bus:

i2c_bus=busio.I2C(SCL,SDA)

Once you have created the I2C interface object, you can use it to instantiate
the RTC object:

rtc=adafruit_pcf8523.PCF8523(i2c_bus)

Date and time

To set the time, you need to set datetime` to a time.struct_time object:

rtc.datetime=time.struct_time((2017,1,9,15,6,0,0,9,-1))

After the RTC is set, you retrieve the time by reading the datetime
attribute and access the standard attributes of a struct_time such as tm_year,
tm_hour and tm_min.

t=rtc.datetimeprint(t)print(t.tm_hour,t.tm_min)

Alarm

To set the time, you need to set alarm to a tuple with a time.struct_time
object and string representing the frequency such as “hourly”:

rtc.alarm=(time.struct_time((2017,1,9,15,6,0,0,9,-1)),"daily")

After the RTC is set, you retrieve the alarm status by reading the
alarm_status attribute. Once True, set it back to False to reset.